Process for the electrolytical production of cyanates from cyanides



many,

' 80% of pure cyanate can 35 in the electrolyte.

always 4 to such a carbonate solution. In this way,

50 which I am able to use,

' Patented Mar. 31, 1925.

UNITED STATES OTTO LIEBKNECHT, OF FRANKFORT ON BOESSL'EB 8c HASSLACHERCOMPANY,

' NEW YORK.

PROCESS FOR THE Ho Drawing.

To all whom it may co'rwe'm:

Be it known that I, O'rlo LIEBKNEGHT, a citizen of the Republic ofGermany, and a resident of Frankfort-on-theMain, Gerhave invented a newand useful for the Electrolytical Production of Cyanates from Cyanidesfor which I filed application in Germany an. 15, 1919), of which thefollowing is a specification.

Paterno & Pannain (Gazetta Chimica Ital. VolrZA (1904) part 2,pages152-155) have described the electrolytic production of alkalicyanates from alkali cyanides. According to their statements, yields ofover he obtained with a cathode current density of 1-4: amps. to 1 dcmwhen working with an electrolyte containing, potassium cyanide 4-6 grammol. liter, potassium hydroxide 1 gram mol.

Process liter.

A part of the cyanate crystallizes out during the electrolysis.

According to their experimental data using 72 g. of potassium cyanidefor oxidation, 32 g. of potassium cyanate crystallized out during thecourse of the electrolysis and 42 more were secured upon evaporating themother liquor. Thus, the greater part of the material must nate due todecompositiom These several disadvantages, I have found can .be avoidedby the use of much greater concentrations of free caustic; alkaliFurther, I have found, that this alkali can be either wholly orpartially replaced by soluble carbonates, especially potassiumcarbonate. -However,

desirable to add some caustic alkali I obtain practically all of thecyanate in solid form directly during the course of the electrolysis andI am thus enabled by the intermittent or constant additions of cyanide45 to make my process a continuous one.

(Note: The solubility of alkali cyanate in a 30% caustic soda solutionis A further advantage of my process results from the large increase ofanode current density being limited only by the current carryingcapacity of the electrodes themselves.

Thus, in my new process using a platinum gauze anode, I am able to usefrom 5000 be obtained by 30 evaporation causing considerable loss ofcyalt IS THE-MAIN, GERMANY, ASSIGNOR TO THE OF NEW YORK, N. Y., ACORPORATION OF ELECTBOLYTICAL PRODUCTION OF (lYANATES FROM C'YANIDES.

Application filed August 27, 1921. Serial No. 496,047.

to 6000 A/M as compared with a current of 100 to 400 A/M used in theearlier process. process, the yield of cyanate drops with increasingcurrent density and a dark colored product of such bad appearances isproduced that the process is not used in commercial practice. On theother hand, by using my new process, even at the very high currentdensities mentioned no decrease in the yield of cyanate is found, and anabsolutely pure white product is obtained. The use of this high currentdensity is of further advantage because of the smaller platinum anodeinvestment required.

Now the greater portion of platinum thus required is used up in theanode connections. Trials to replace this platinum by other metals didnot succeed at first. The strong alkali of the electrolyte make the useof aluminum and zinc out of the question. Nickel and iron answered thispurpose without serious metal losses but gave a discolored product ofinferior quality, and at a considerably decreased current efiiciency.Copper was then tried and found to be a suitable metal both for currentdistributors and connectors, the cyanate so obtained being white whilethe current yield equalled that when only platinum was used. In otherdetails the apparatus can be constructed as described in the literature.

Preferably the electrolyte is continuously kept nearly saturated withcyanide during electrolysis, except when concluding a run, when all thecyanide present is oxidized to cyanate, thereby decreasing the losses ofcyanide in the mother liquor.

As an illustration of the process, the following experiment isdescribed. The electi olyte consists of 3 liters of a 27% solution ofcaustic soda, together with the given quantity of sodium cyanide whichit is desired to oxidize to cyanate. This can either be added at onetime up to saturation or at intervals during the course of theelectrolysis. gauze or screen of 100 cm area. The cathodes consist ofiron. A current of 65 amperes is used. The temperature of theelectrolyte should be maintained at about C. When the calculatedqu'antit of current needed to convert the cyani e to cyanate has beensupplied, the electrolysis The anode consists of platinum In addition tothis, with the former Ina is discontinued. The electrolyte is thencooled to 1012 (3., and the cyanate is recovered by filtering, anexcellent current and material yield being secured.

What I claim is:

1. A process for production of alkali cyanates by electrolysis of analkaline solution containing cyanides.

2. A process for production of alkali cyanates by electrolysismf analkaline solution containing cyanides and more than one gram mol. perliter of combined caustic alkali and alkali carbonate.

3. A process for production of alkali cyanates by electrolysis of analkaline solution containing cyanides at a current density of more than400 amperes per square meter.

4. A process for production of alkali cyanates by electrolysis of analkaline solution containing eyanides using copper as the anodicconducting and distributing member.

5. A continuous process for the production of alkali cyanates byelectrolysis of an alkaline cyanide solution,

being removed periodically.

6. A continuous process for the producmore cyanide be ing added and theprecipitated cyanate tion of alkali cyanates by-electrolysis of analkaline cyanide solution, containing more than one gram mol. ofcombined caustic alkali and alkali carbonate, more cyanide being addedand the precipitated eyanate being removed periodically.

A continuous process for the production of alkali cyanates byelectrolysis of an alkaline cyanide solution, at a current density ofmore than 4.00 amperes per square meter, more cyanide being added andthe precipitated cyanate being removed periodically.

8. A continuous process for the production of alkali cyanates byelectrolysis of an alkaline cyanide solution, the anodic conducting anddistributing member, more cyanide being added and the precipitatedcyanate being removed periodically.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

OTTO LIEBKNECHT. Witnesses:

THEODOZR PoHL, EMIL SOHELLER.

using copper as

